1. Field of the Invention
This invention relates to a cooling assembly for electric parts, and more particularly to an improved cooling assembly for electric parts.
2. Description of the Prior Art
Generally, high power semiconductor elements such as power transistors and diodes are used as circuit elements in acoustic apparatus such as stereo amplifiers and television receivers, or in electronic apparatus such as transmitters, measuring apparatus and rectifiers. Most of the consumed power is converted into thermal energy in the high power semiconductor elements. There is the possibility that the high power semiconductor elements will be heated up and damaged. Accordingly, a cooling apparatus is provided for the high power semiconductor element for radiating heat outwards from the high power semiconductor element. Generally, a heat sink having fins, made of aluminium is used as the cooling apparatus. However, the distance between the fins of the heat sink and the heat-generating element is a long distance, and the thermal resistance of the cooling system is high. Accordingly, a satisfactory cooling effect cannot be obtained by the heat sink. The heat sink having fins is relatively large. The space occupied by the heat sink is relatively large in the electronic apparatus which is undesirable.
Recently, a heat pipe has been used as a heat transfer means for heat radiation for an electronic apparatus. The heat transfer means for heat radiation comprises a closed cylindrical pipe made of copper with closed ends. The inner wall of the pipe is lined with netted wicking material impregnated with working fluid (for example, water) as a heat conveying medium. The interior of the pipe is decompressed so that the working fluid can be easily vaporized.
The heat pipe consists of a vaporizing portion, an adiabatic portion and a condensing portion. When heat input power is supplied to the vaporizing portion of the heat pipe from the semiconductor element, the working liquid in the vaporizing portion is supplied heat of vaporization and vaporizes. The vapor pressure of the vaporizing portion increases with the vaporization of the working liquid. The vapor flows to the adiabatic portion of lower vapor pressure from the vaporizing portion, and then it reaches the condensing portion through the adiabatic portion. In the condensing portion, the vapor is cooled and condensed to radiate heat of liquefaction. With the movement of the vapor which has obtained heat of vaporization, heat from the semiconductor element as a heat-generator is transferred in the axial direction of the heat pipe. Thus, heat is radiated outward from the semiconductor element.
The amount of the working liquid in the vaporizing portion is smaller than the amount of the working liquid in the condensing portion, since the working liquid is always vaporized in the vaporizing portion and the working liquid is always condensed in the condensing portion. Accordingly, the capillary pressure in the condensing portion is higher than the capillary pressure in the vaporizing portion. Due to the capillary action of the wicking material, the working liquid is transported from the condensing portion to the vaporizing portion. The working liquid is continuously vaporized and condensed nearly at the same temperature, respectively. The temperature gradient of the heat pipe is very small over the whole length of the heat pipe in the stationary state. A large amount of heat is transferred. The thermal conductivity of the heat pipe is high, or the thermal resistivity is low.
For cooling, the semiconductor element is attached to a mounting plate or a polygonal metal block fixed directly to the vaporizing portion of the heat pipe by welding or the like. After lead-wires are connected to the semiconductor element thus attached, the semiconductor element must be accompanied by the heat pipe when the semiconductor element is to be moved from one place to another. Or whenever the semiconductor element is to be moved, the lead wires must be disconnected from the semiconductor element. When the heat pipe or cooling fins attached to the heat pipe are large it is very troublesome to move the semiconductor element. When the semiconductor element is attached to the metal block, the lead wires must be detoured, and cannot be connected directly to a printed circuit board.
Although the heat pipe is superior in thermal conductivity, the thermal conductivity is lowered with the reduction of the diameter of the heat pipe and with the length of the latter. It is troublesome to handle the long heat pipe. There are thus various problems relating to the heat pipe.
As understood from the above description relative to the operation, it is not easy to cut the heat pipe to a required length for use. Accordingly, it is required that the length of the heat pipe be standarized for any case.